I installed Windows 7 simply because Sketchup Make refuses to run properly under Wine.
I used Gparted to resize and make a new partition /dev/sda3, leaving(I HOPE!) Ubuntu 12.04 on the original (resized /dev/sda1). Windows boots up and runs fine, but I don't know how to get back into Ubuntu.
I did at one stage get a screen which offered me a choice of OS - Win 7 or BLANK, Ubuntu was not there.
Have made a copy of all my Ubuntu files etc on an external HDD, but I could use some help getting back into Ubuntu!

I try to treat the cause, not the symptom. I avoid the terminal in instructions, unless it's easier or necessary. My instructions will work within the Ubuntu system, instead of breaking or subverting it. Those are the three guarantees to the helpee.

Thank you. Now have CD of Boot Repair, booted from it and followed its instructions; sadly, although I now have a screen giving me options to boot into Ubuntu (normal or repair modes), some other options and Win7. The ONLY one which results in a booted OS is Win7, very smooth. Choosing Ubuntu give a screen 'running in low definition' or similar wording with 4 options listed, only the top one 'run in this definition once', or something similar is selected (the others cannot be selected). 'Enter' gives a further screen at which point the system freezes, the only option being a 'hard shut down'.
Sorry to be a bit vague about screen contents but of course I can't take screen shots nor open the sequence whilst using Win 7 to get to this forum!
It would seem that my Ubuntu 12.04 installation is still in /dev/sda1 but I can't get it running. As I have copies of all the important 12.04 system files, I could, in the worst case format the sda1 partition and reload Ubuntu - perhaps moving on to 13.04. Trouble is I don't feel competent to do all that without a 'guiding hand'.
In a nutshell, I'm stuck and could use some help.

I would suggest booting into Gparted from a live boot or live boot something like Ubuntu so you can do some partitioning. If you have backed up all your files and aren't worried about starting over, I would just delete the partition on /dev/sda1 and making a new Linux partition for 13.04. I'm going to use fdisk, since I'm more familiar with that rather than Gparted which means you would need to live boot Ubuntu, to begin you will need root privileges so use "sudo" (Also note that I'm using sdc as an example, you would type sda):

Code:

sudo fdisk /dev/sdc

You should see "Command (m for help)" and if you press "m" you will see:

Since we want to delete the first partition, type "d", I have only one partition on my example drive, but it would ask which partition number 1-4 and you would type "1".

Now we should have three available primary partitions to use. Lets now create a new primary partition, so type "n", then "p" for primary, then "1" for first partition, then take the default first sector by pressing enter, then the default last sector or +size example below:

On the question about the Last Sector, this is where you specify how large that partition will be. So if you wanted to use the same exact size of your first Ubuntu install, then you would type(We will use 50GB for example):

Now we have successfully deleted and created a new partition, so we must now give the partition a type. Type "p" to list the partition, and if the new partition has an ID of 83 and a System of Linux, then you don't have to worry about creating a type, but for the sake of it (Note that you can type "l" to list all the FS types, but for Ubuntu, the Hex code 83 will work.):

Thank you. I decided to use the gparted route as it seemed simpler to a dumbo like me!
Result! - However I now have Win 7 in an ntfs partition and Ubuntu 13.04 in an ext4 prtition, both work fine but the Ubuntu partition is too small. There are two other 'Volumes ' listed in the Ubuntu file system, one of 24GB which I assume from its contents to be the Win 7 one and another of 210GB which I don't seem to be able to access from either OS.
Have tried to use fdisk to show me more but get confused - man fdisk and help are a bit too obscure for me I regret.
The screenshot of 'Details' shows the HDD as only 13.1GB, Screenshot from 2013-12-18 23:23:47.png I assume this refers to the Ubuntu 'volume??' only. Actual HDD total is 320GB.

Result! - However I now have Win 7 in an ntfs partition and Ubuntu 13.04 in an ext4 prtition, both work fine but the Ubuntu partition is too small. There are two other 'Volumes ' listed in the Ubuntu file system, one of 24GB which I assume from its contents to be the Win 7 one and another of 210GB which I don't seem to be able to access from either OS.

.............Actual HDD total is 320GB.

According to 'parted -l', your HDD is 250GB and not 320GB as you think.
Your 2nd partition NTFS is Windows (23.7Gb) and your partition No.5 is Linux swap (3Gb).

There are two Linux partitions, partition No. 1 (210Gb), and No. 6 (13.5Gb).
Not sure which of the two is your '/' root partition. Post the output of: